Ester oil compositions containing acid anhydride



United States Patent Ofi 3,090,753 Patented May 21, 1963 ice 3,090,753 ESTER OIL COMPOSITIONS CONTAINING ACID ANHYDRIDE Alfred H. Matuszak, Westfield, George J. Allen, Roselle,

and Stephen J. Metro, Scotch Plains, N.J., assiguors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Aug. 2, 1960, Ser. No. 46,878 3 Claims. (Cl. 25242.7)

Because of their utility over extremely wide temperature ranges, the synthetic ester lubricating oils are widely used in the formation of lubricants for aircraft engines such as turbo-jet, turboprop and pure-jet aircraft. In such engines, lead-containing bearings are used and unfortunately, the synthetic esters per se are corrosive to such bearings. The present invention resides in the discovery that acid auhydrides may be directly added to ester oils in order to inhibit lead corrosion. At the same time, the anhydrides do not detract from the other desirable properties of the ester oil. In fact, the anhydrides tend to enhance other important properties of the composition, particularly the load-carrying ability of the oil.

The acid anhydrides of the invention include monoor dianhydn'des of carboxylic acids, particularly of hydrocarbon acids, i.e. where the entire molecule is made up of carbon and hydrogen except for the oxygen of the anhydride portions, containing about 8 to 50, preferably 8 to 30 carbon atoms per molecule. Such anhydrides will include those of aromatic, alicyclic, aliphatic, alkaryl, and other acids. Examples of these anhydrides include pyromellitic dianhydride, alkenyl succinic anhydride, phthalic anhydride, dialkyl pyromellitic monoanhydride, hemimellitic 'anhydridc, trimellitic 'anhydride, naphthalic anhydride (1,8), prehnitic dianhydride, diphenic anhydride, and mellitic dianhyd-ride.

The lubricants of the invention will comprise a major amount of an ester oil and dissolved therein, about 0.001 to 5.0 Wt. percent, preferably 0.01 to 2. wt. percent, based upon the total amount of the lubricant, of anhydride.

The ester oils operable as base oils in the compositions of this invention comprise hydrocarbon chains interruped with 2 to 10 ester linkages, and which can be further interrupted with ether or thioether linkages. Included are diesters, polyesters, and complex esters.

The diesters are generally prepared from dicarboxylic acids fully esterified with monohydric alcohols, or from glycols fully esterified with rnonocarboxylic acids. The total number of carbon atoms in the diester molecule is generally about 18 to 36, preferably 20 to 28.. Preferred dicarboxylic diesters are those of the formula:

wherein each R may be the same or different and represents the straight or branched chain alkyl radical of a monohydric alcohol having about 6 to 13 carbon atoms, While R is a straight or branched chain C to C divalent saturated aliphatic hydrocarbon radical. Examples of such diesters include: di-2-ethylhexyl sebacate, di-C Oxo sebacate, di-nonyl sebacate, di-2,2,4-trimethylpentyl 2 sebacate, di-2-ethylhexyl azelate, di-2,2,4-trimethylpentyl azelate, di-C 0x0 azelate, di-n-heptyl isosebacate, di-C OX0 :adipate, \di-nonyl adipate, di-C 0x0 adipate, di-2- ethylhexyl adipate, mono C Oxo, mono C Oxo adipate, dl-Cq Oxo adipate, di-C trimethyl adipate, di-C Oxo pimelate, etc. Other operable diesters are those prepared from glycols and monocarboxylic acids such as dipropylene glycol dipelargonate and polyethylene glycol 200 dicaproate. Diesters prepared the 0x0 alcohols, which are isomeric mixtures of branched chain aliphatic primary alcohols, are particularly desirable. The Oxo alcohols have a very high degree of branching in the hydrocarbon chain, which results in diester oils having low pour points and low visoosities at low temperatures. These alcohols are prepared from olefins, such as polymers and copolymers of C and C monoolefins, which are reacted with carbon monoxide and hydrogen in the presence of a cobalt-containing catalyst such as a cobalt carbonyl, at temperatures of about 300 to 400 F., and under pressures of about 17000 to 3000 psi. to form aldehydes. The resulting aldehyde product is then bydrogenated to form the 0x0 alcohol which is then recovered by distillation from the hydrogenation product.

Operable polyesters are prepared by reacting polyhydric alcohols such as tn'methylolpropane and pentaerythritol with monocarboxylic acids such .as butyric acid, caproic acid, caprylic acid, pelargonic acid, etc. to give the corresponding trior tetraestens.

The complex esters which may be used as the base oils are formed by esterification reactions between a di carboxylic acid, a glycol, and an alcohol and/or a monocarboxylic acid. These esters may be represented by the following formulas:

wherein: R and R are alkyl radicals of a monohydric alcohol or a monocarboxylic acid; R and R are hydrogen radicals of dicarboxylic acids, e.g. alkandioic acids; and R and R are divalent hydrocarbon or hydro carbon-oxy radicals, such as -CH (CH or -CH CH (O CH CH or CH CH CH OCH CH (CH derived from an alkylene glycol or polyalkylene glycol. n in the complex ester molecule will usually range from 1 to 6 depending upon the product viscosity desired which is controlled by the relative molar ratio of the glycol or polyglycol to the dicarboxylic acid. In preparing the complex ester, there will always be some simple ester formed, i.e. n=0, but this will generally be a minor portion.

Some specific materials used in preparing the above types 'of complex esters are as follows: alcohols having 6 to 13 carbon atoms such as nbutyl alcohol, 2-ethylbutyl alcohol, 2-ethylhexano1, n-hexyl alcohol, C Oxo alcohol and C Oxo alcohol, etc.; the corresponding fatty or monocarboxylic acids; C to C dicarboxylic acids such as sebacic, adipic and azelaic; and glycols such as polyethylene glycol. In general the complex esters will have a total of 20 to 80, preferably 40 to 65, carbon atoms. These complex esters and methods for their preparation are known in the art and have been described in various patents.

The composition can also include other additives (e.g. 0.01 to 10.0 wt. percent). Included are oxidation inhibitors such as phenothiazine, dioctyl phenothiazine, dioctyl diphenylamine, phenyl u-naphthylamine, p-amino diphenyl amine; viscosity index improvers such as polymethacrylates, polystyrene; anti-foamant-s such as dimethylsilicone polymers; anti-wear agents such as tricresyl phosphate; load-carrying agents; etc.

Particularly, desirable load-carrying agents are various alkylene glycol titanates. These materials may be represented by the general formula:

where R is an aliphatic radical having from about 3 to 15, and preferably from 6 to 12, carbon atoms. It is, of course, possible for both hydroxyl groups of one glycol to react with two of the acidic groups of titanic acid molecules to form polymeric materials.

The more probable formulae for the glycol titanates are for the monoglycol or diglycol titanates, respectively, where R is the aliphatic radical of the glycol as heretofore stated.

Alkoxy glycol titanates are also contemplated, represented by the formula:

)6? a an D 0R 0 where R is the aliphatic radical of the glycol as heretofore stated and R is an aliphatic radical of from 3 to 12 carbon atoms, e.g. dibutoxy di(hexylene glycol) titanate.

Specific examples of the titanates include hexylene glycol titanate, dodecylene glycol titanate, octylene glycol titanate, and dibutoxy di(hexylene glycol) titanate. Titanates of the preceding types are known in the art and have been described in various patents, e.g. U. S. Patent No. 2,643,262.

The titanates are preferably used in amounts of 0.01 to 5.0 wt. percent as load-carrying agents. While extremely effective for carrying load, titanates are very corrosive to copper and lead. Although conventional lead and copper corrosion inhibitors were not effective with titanates, the anhydrides of the present invention are efiective.

The present invention will be further understood by reference to the following examples which include preferred embodiments of the present invention:

EXAMPLE I A base oil material was prepared consisting of 100 parts by weight of 50 volume percent of a di-C Oxo adipate and 50 volume wt. percent of di-C Oxo adipate, and 1 part by weight of phenothiazine as an antioxidant.

To the above base oil was added pyromellitic dianhydride, and/ or an alkylene glycol titanate in various amounts. The titanate was a solution of about 30 wt. percent n-butyl alcohol and about 70 wt. percent of tetra- (octylene glycol) titanate prepared by transesterification' of one molar amount of tetra n-butyl titanate with four molar amounts of Z-ethyl-hexane diol. This was a commercial product sold by DuPont under the tradename OGT-41. The resulting blends were then tested for lead corrosion inhibition in accordance with the MILFL- 7808 specification procedure. This test procedure is carried out by rapidly rotating a weighed bi-rnetallic strip, consisting of a lead strip and a copper strip bound together, in the oil sample maintained at 325 F. while air is bubbled through the sample. The weight loss of the strip is determined in terms of milligram weight loss per sq. inch of lead surface at the end of l, 4, 8 and 12 hours of operation. The compositions prepared and the results obtained are summarized in Table I, which follows:

Table I EFFECT OF PYROMELLITIO DIANHYDRIDE (PMDA) ON LEAD CORROSION Lead corrosion test loss in mgJin.

1 hour 4 hours 8 hours l2h0urs A. Base 0. 4 0. 6 0. 6 1. 8 B. A plus 0.05 weight percent PMDA 0 0 O 0 C. A plus 1 weight percent tetra- (octylene glycol) titanate 65 195 454 750 D. 0 plus 0.1 weight percent PMDA- 0 0 30 220 E. 0 plus 0.2 weight percent PMDA- 0 0 0 0 F. 0 plus 0.3 weight percent PMDA 0 0 1 1 G. CplusOAweightpercentPMDA 0.2 0.4 16 51 H. A plus 3 weight percent tetra- (octylene glycol) titanate 37 172 477 798 I. H plus 0.1 weight percent PMDA 25 124 447 788 J. H plus 0.2 weight percent PMDA- 0 4 36 441 K. H plus0.3 weight percent PMDA- 1 42 323 682 L. Hplus0.4weightpercentPMDAL 0 0 8 400 1 50 vol. plercent di-Cw Oxo adipate, 50 vol. percent (ii-C3 0x0 adlpate plus 1 weig t percent phenothiazine.

2 Some PMDA precipitated.

EXAMPLE II An ester oil mixture was prepared consisting of 50 volume percent di-C 0x0 adipate and 50 volume percent of di-C Oxo adipate. To this oil mixture was added 0.5 wt. percent phenothiazine as antioxidant, and 0.001 wt. percent of a diamethyl silicone having a viscosity of 60,000 cs. at 25 C. as an antifoamant. To this base oil composition was added 0.6 wt. percent of a C alkenyl succinic anhydride having the formula:

CHrO

The base oil composition per se and the base oil composition containing the succinic anhydride were tested in the lead corrosion test previously described above, and in an oxidation-corrosion test which determined the oxidative stability and the corrosivity of the compositions to copper, magnesium, iron, aluminum and silver. These tests were carried out in accordance with MlLL-7808C specification procedures. In the oxidation-corrosion test, weighed strips of the metals to be tested were immersed in cc. of the oil sample maintained at 347 F. for 72 hours while 0.5 liter per hour of air was bubbled through the sample. The metal strips were then reweighed to determine the corrosivity of the oil as indicated by the weight change in mg./cm. The oxidative stability of the oil was shown by the change in viscosity and neutralization number of the oil after testing.

The results of the above tests are summarized in Table II which follows:

Table II EFFECT OF Ca ALKENYL SUCOINIO ANHYDRIDE Adipate Adipate base base 1 plus 0.6%

anhydrlde Lead corrosion te t m [in 4 hrs. 21 0 8 hrs. 89 0 12 hrs 340 1. 2 347 F. oxidation corrosion test:

A neut. numbeL- 0. 87 0. 47

A vis./100% 3. 6 2.0

1 Adipate Base: 50 vol. percent C! 0x0 adipate plus 50 vol. percent 010 0x0 adipate plus 0.5 weight percent phenothiazine plus 0.001 weight percent -200 (60,000 cs.) silicone.

EXAMPLE III A base oil composition consisting predominantly of di-C /C OX0 adipate and di-octyl sebacate plus various lubricating oil additives Was prepared and stored for six months, during which time it had developed a high corrosivity toward lead. To samples of this highly corrosive base oil were then added phthalic anhydride and pyromellitic anhydride to determine their eifect on reduoing the lead corrosion of the base oil. From the results shown in the following table it will be noted that each anhydride inhibits the lead corrosivity of the base oil but that the pyromellitic dianhydride is more effective than the phthalic anhydride. This is also true when the corrosive oil is stored under high temperature conditions for 14 days.

Table III EFFECT OF PHIHALIC ANHYDRIDE AND PYROMELLITIC DIANHYDRIDE ON LEAD CORROSION It has been found that when the acid anhydride is to be used with an alkylene glycol titanate, excellent results are also obtained upon heating the titanate and anhydride to temperatures of about 275 to 325 F. for about 0.1 to 1.0 hour. It is believed that this heating results in the formation of a complex between the glycol titanate and the anhydride. Alternatively the two materials may be mixed cold, i.e. at room temperature in the ester oil relying upon the heating of the lubricating oil during use to help promote the reaction.

100 grams of the previously described tetra (octylene glycol) titanate prepared from 2-ethylhexane diol was dissolved in 100 grams of di(C Oxo) adipate and the solution heated to 300 F. to remove much of the diluent n-butyl alcohol introduced with the titanate. At this point 10 grams of pyromellitic dianhydride was added and stirred into the mixture. The mixture was then further heated for about 0.3 hour. Upon cooling, the resulting complex titanate solution Was then used in formultaing two lubricating oil blends as follows:

Blend A.The blend was prepared, wherein all parts are by weight, by simple mixing of 100 parts of di(2 ethylhexyl) sebacate, 1 part phenothiazine, 0.001 part of silicone anti-foamant and 0.7 part of the solution of complex of octylene glycol titanate and pyromellitic dianhydride. The composition carried 3,765 pound/inch load in the Ryder gear test and showed no corrosion in the lead corrosion test after 12 hours. On the other hand, the sebacate ester without the complex will carry only about 1,900 lb./in. in the Ryder gear test, while the addition to the titanate per se to the ester oil would result in severe lead corrosion.

Blend B.-To parts by Weight of a 50/50 volume mixttue of di(C Oxo) adipate and di(C 0x0) adipate was added 0.7 part by weight of phenothiazine and 0.7 part by weight of the solution of complex ti-tanate. This composition carried 3,440 1b./in. load in the Ryder gear test. It also showed only 5.0 mg./in. weight loss in the lead corrosion test at the end of 12 hours, which is within acceptable limits.

In sum, the present invention includes the addition to lubricating oils of monoand di-anhydrides of the formula: R(X) where R is a hydrocarbon radical, X is the anhydride group and n is one or two. R can also include a carboxylic acid group substituted on the hydrocarbon chain. The total number of carbon atoms in the molecule will be 8 to 50, e.g. 8 to 30. As a further aspect of the invention, heating the anhydride with alkylene glycol titanates, either mono-, di-, tri-, or tetratitanates or mixtures thereof results in some sort of a complex which is particularly useful as a load-carrying agent with low corrosivity to lead.

What is claimed is:

1. A synthetic ester lubricating oil composition comprising a major proportion of carboxylic acid ester lubricating oil and about 0.001 to 5.0 wt. percent of pyromellitic dianhydride.

2. A synthetic ester lubricating oil composition according to claim 1, which also contains about 0.01 to 5 .0 wt. percent of an alkylene glycol titanate prepared from C to C aliphatic glycol.

3. A lubricating oil composition comprising a major proportion of diester of the formula:

ROOCRCOOR wherein R represents a C to C alkyl radical and R is a C to C aliphatic hydrocarbon radical, and about 0.001

to 5.0 wt. percent based upon the total composition, of pyromellitic dianhydride.

References Cited in the file of this patent UNITED STATES PATENTS 2,334,158 Von Fuchs, et a1. Nov. 9, 1943 2,788,326 Bondi et al. Apr. 9, 1957 2,806,860 Phillips et al. Sept. 17, 1957 2,809,160 Stewart et a1 Oct. 8, 1957 2,960,469 Young et al Nov. 15, 1960 FOREIGN PATENTS 809,198 Great Britain Feb. =18, 1959 

1. A SYNTHETIC ESTER LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PROPORTION OF CARBOXYLIC ACID ESTER LUBRICATING OIL AND ABOUT 0.001 TO 5.0 WT. PERCENT OF PYROMETALLITIC DIANHYDRIDE. 